Coking processes, especially the delayed coking process, provide a way of converting high boiling and refractory petroleum residua to more valuable, lower-boiling products with petroleum coke being obtained as a by-product. In recent years, it has been found that it may be desirable to subject the coker feedstock or a recycle stream to hydrotreating in order to improve the operation of the process or to obtain products of better quality. For example, hydrotreating in this way may bring about a decrease in coke yield with a consequent increase in the liquid and gas product and in the coker throughput; it may also result in a coke product of higher purity with a reduced heteroatom content which may be sold as higher value metallurgical or electrode grade material. U.S. Pat. No. 4,213,846, for example, describes a process in which the recycled gas oil from the coker is hydrotreated to produce a premium type coke. U.S. Pat. Nos. 3,684,688, 3,617,481 and 3,891,538 also describe the use of hydrotreating in combination with coking processes.
Processes have also been proposed for carrying out coking in the presence of coal, coal chars, carbon fines and other solids. U.S. Pat. Nos. 2,717,865, 2,775,546, 2,899,376, 3,673,080 and 4,082,650 describe processes of this kind. U.S. Pat. No. 4,259,178 describes a process for the delayed coking of heavy petroleum residual materials blended with a coking or non-coking coal. The coke product is stated to be of a softer and more porous, friable quality.
Contemporary coditions in the world petroleum market have made it desirable to improve the useful liquid yield from coking and other residual treatment processes in order to maximize the yield of economically valuable products such as distillates and gasoline. At the same time, it has become desirable for countries with major coal reserves to utilize that resource to a greater extent than in the past and this, in general, means that improved coal liquefaction and gasification processes must be found for producing liquid and gaseous fuels which are more desirable than solid fuels which, by and large, can be used effectively only in large installations such as electrical power plants.